2, 6-bisalkyldithio-1, 4-pyrone



United States Patent 2,983,733 2,6-BISALKYLDITHIO-1,4-PYRONE Clyde S. Scanley, Stamford, Conn., and Ellis K. Fields,

Chicago, Ill., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana No Drawing. Original application Jan. 11, 1955, Ser. No. 481,267, now Patent No. 2,897,153, dated July 28, 1958. Divided and this application Aug. 18, 1958, Ser. No. 755,377

4 Claims. (Cl'. 260-327) This invention relates to 2,6-polythio-l,4-thiopyrones as; new compositions of matter; It relates in particular to oil soluble thiopyrones which impart resistance to oxidative deterioration when incorporated in lubricating oil compositions, and which have been described in our pending application, Serial Number 481,267, filed January 11, 1955, of which this application is a division, now Patent No. 2,897,153.

Many of the more successful oxidation inhibitors for lubricating oil use contain elements or chemical groups which are essential in contributing protection for the lubricant against oxidative deterioration but which contribute corrosive properties to the lubricant against certain metals. Thus, a useful and highly active bearing corrosion inhibitor is sulfu-rized dipentene. Because of its sulfur content in active form, however, sulfurized dipentene may be corrosive to silver or copper bearing surfaces under some conditions of use. Since this is disadvantageous in some types of service, particularly for use as a diesel lubricant, alternative bearing corrosion inhibitors of satisfactory activity without, corrosive properties towards silver are desired.

We. have discovered that 2,6-polythio-1,4-thiopyrones have value as inhibitors against oxidative corrosion when incorporated in lubricant compositions. They have particular value as hearing corrosion inhibitors and, because they are non-corrosive to silver in lubricant compositions, have a wide range of applicability. They also have value as extreme pressure lubricating additives. The thiopyrones of our invention are characterized by the presence of disulfide or polysulfide organic groups in the 2,6- position of the thiopyrone ring structure and contain sufiicient carbon and hydrogen in the form of alkyl or hydrocarbon substituted alkyl groups to provide oil solubility. They are believed to have the following structural formula:

R -S srRa.

In the formula, R and R may be hydrogen, alkyl, aryl, aralkyl, or substituted modifications thereof. R and R represent replacement or partial replacement of hydrogen by hydrocarbon groups, particularly of the type imparting oil solubility such as alkyl groups and substituted alkyl groups such as naphthene and aromatic substituted alkyl groups. The subnomials x and y represent integers of two or more.

The polythio-thiopyrones are produced from 2,6-dimercapto thiopyrones, advantageously by reaction with a sulfenyl halide. The 2,6-dimercapto thiopyrones are readily produced by reaction of ketones with carbon disulfide in the presence of a strong alkalisuch aspotash or caustic soda. substituted aliphatic ketone having four active hydro- The ketone may be any aliphatic, or.

gens on the a and a carbon atoms. For example, actone, methyl ethyl ketone, benzyl ketone are convenient starting ketones whereas acetophenone or benzophenone are not suitable. Substituted ketones may be used, provided that for use as lubricating oil additives they do not introduce functional substituents which are incompatible with or unsuited to the lubricant formulation. An example of available substituted ketones of value are the esters of acetone dicarboxylic acid, e.g., the ethyl esters, which are readily derived from citric acid.

The 2,6-dimercapto thiopyrones are converted readily to the polythio-thiopyrones of the invention by reaction with a sulfenyl halide. The reaction may be conducted, for example, in an organic medium, e.g., carbon tetrachloride, at a temperature of about 0 to 10 C. The sulfenyl halide, usually the chloride for convenience, is selected with a view to imparting the desired degree of oil solubility to the finished inhibitor. For this reason, aliphatic sulfenyl chlorides having chain lengths of four carbon atoms or more are preferred, for example, n-butyl, t-octyl, dodecyl and the like. The aliphatic grouping, however, may comprises a substituted aliphatic such as naphthenic or aromatic substituted aliphatic chains as in 3-cyclohexylpropylsulfenyl chloride or benzyl sulfenyl chloride, and in general, may contain from one to twenty carbon atoms. Thme sulfenyl chlorides are readily de rived from the corresponding mercaptans by chlorination. The polythio-thiopyrones also may be produced from 2,6-mercapto thiopyrone by reaction with a mercaptan and sulfur or by reaction with a mercaptan and a sulfur halide such as sulfur monochloride.

The new products are viscousliquids of varying oil solubility depending upon the amount and nature of hydrocarbon substitution in the structure and the nature of the base oil. In general, it is desirable that the polythio-thiopyrones contain eight or more carbon atoms in the form of aliphatic substituents in order to provide adequate oil solubility for use as lubricating oil additives in the manner described in our above-referred to application. Thus, it is usually desirable in preparation to employ an alkyl or substituted alkyl sulfenyl halide pro viding at least 4 carbon atoms in the alkyl chain and to react the dimercapto thiopyrone intermediate with the stoichiometric proportion, or a slight excess, of a sulfenyl halide. Alternatively, longer chain ketones can be selected as starting materials in the preparation of the di mercapto thiopyrone intermediate. The products then can be handled in the form of mineral oil concentrates which facilitate handling in the formulation of commercial lubricating oils and greases. The level of use in the finished lubricants, however, is usually quite small. For use as an oxidation inhibitor in a hydrocarbon oil susceptible to oxidative deterioration the concentration of the additive may be in the range of about 0.001 to 1 percent by weight. For use as a bearing corrosion inhibitor in crank case lubrication, the inhibitor is used in the range of about 0.005 to 5 percent by weight. For use as. an additive to impart extreme pressure lubricating properties to mineral oil lubricants, the additive is used in the range of from about 0.1 to about 10 percent by weight.

In commercial formulation, the polythio-thiopyrone additives will ordinarily be used, as is customary in conjunction with other, compatible lubricating oil additives, for example, pour depressants, viscosity index improvers, anti-rust agents, anti-foam agents and the like. The base may comprise any hydrocarbon oil subject to oxidative deterioration. For most applications, the oil will comprise a mineral oil fraction ofthe. usual viscous lubricating oil range.

As produced by reaction of a.2,6-dimercapto thiopyrone with a sulfenyl halide, the product is a 2,6-dithio-1,4-

aoearas thiopyrone. We have further found that additional sulfur can be incorporated at the disulfide linkage by direct sulfurization so that a variety of polysulfide derivatives can be readily prepared. The sulfurization is conducted at a temperature at about 115 to about 200 C., by reaction of the thiopyrone with sulfur for a period ranging from a few minutes to several hours. The resulting polysulfide derivatives in general show improved extreme pressure lubricating properties as well as hearing corrosion inhibitors.

We also have found that the 2,6-polythio-l,4-thiopyrones may be used with advantage as inhibitors in certain crank case lubricants of the heavy duty type in conjunction with oxidation inhibitors of the active sulfur type. When used in ratios ranging from about 20:1 to 1:20 of thiopyrone to active sulfur type inhibitors, e.g., sulfurized dipentene, the thiopyrones appear to promote stability against oxidative deterioration and, at the same time, to function as deactivators of the active sulfur type inhibitors with respect to corrosive tendencies toward silver and copper bearing surfaces.

The invention will be further illustrated by means of specific examples. In the examples, the new additives were evaluated by means of a stirring sand corrosion test (SSCT) and the well-known EMD silver bearing corrosion test.

The SSCT test was run as follows: A copper-lead test specimen is lightly abraded with steel wool, washed with naphtha, dried and weighed to the nearest milligram. The cleaned copper-lead test specimen is suspended in a steel beaker, cleaned with a hot tri-sodium phosphate solution, rinsed with water and acetone and dried. 250 grams of the oil to be tested together with 0.625 gram lead oxide and 50 grams of a 30-35 mesh sand are charged to the beaker. The beaker is then placed in a bath or heating block and heated to a temperature of 300 F. (L -2 F.) while the contents are stirred by means of a stirrer rotating at 750 r.p.m. The contents of the beaker are maintained at this temperature for twenty-four hours, after which the copper-lead test specimen is removed, rinsed with naphtha, dried and weighed. The test specimen is then replaced in the beaker and an additional 0.375 gram of lead oxide added to the test oil. At the end of an additional twenty-four hours of test operation the test specimen is again removed, rinsed and dried as before, and weighed. The test specimen is again placed in the beaker together with an additional 0.250 gram of lead oxide and the test continued for another twentyfour hours (seventy-two hours total). At the conclusion of this time, the test specimen is removed from the beaker, rinsed in naphtha, dried and weighed. The loss in weight of the test specimen is recorded after each weighing. A weight loss of 200 mg. or less in 48 hours and 500 mg. or less in 72 hours is allowable.

In the EMD test a silver strip 2 cm. x 5.5 cm. with a small hole at one end for suspension is lightly abraded with No. steel wool, wiped free of any adhering steel wool, washed with carbon tetrachloride, air-dried and then weighed to 0.1 milligram. Three hundred cc. of.

the oil to be tested is placed in a 500 cc. lipless glass beaker and the oil is heated to a temperature of 300 F. (:2" F.) and the silver test strip suspended in the oil so that the strip is completely immersed therein. The oil in the beaker is stirred by means of a glass stirrer operating at 300 rpm. At the end of twenty-four hours, the silver strip is removed and while still hot rinsed thoroughly with carbon tetrachloride and air-dried. The appearance of the strip is then visually noted and given ratings according to the following scale:

. 1Bright .2-Stained 3-Grey-black. 4-Black, smooth 5-Black, flake til 4 After the visual inspection the silver strip is immersed in a 10% potassium cyanide solution at room temperature until the silver surface assumes its original bright or silver appearance. The silver strip is then washed successively with distilled water and acetone, air-dried and weighed. A weightloss of 20 mg. or less is considered passing.

Example I 2,6-dimercapto-3-methyl-l,4-thipyr0ne was prepared as follows:

A mixture of 50 g. methyl ethyl ketone and 200 g. carbon disulfide was cooled to 10 C. and treated with 150 g. powdered potassium hydroxide. After 30 minutes, the temperature rose to 35 C. Stirring was started. Carbon disulfide refluxed vigorously as the temperature went to 47 C. for a period of 20 minutes. The mixture was cooled to room temperature, excess carbon disulfide and ketone was decanted from the solid, and the solid was washed with cc. ether. The solid was taken up in water, the solution acidified with hydrochloric acid, and the precipitated solid collected on a filter. It was purified by dissolving in 10% aqueous sodium acetate, filtering, and acidifying the solution. The red crystals were collected on a filter, washed with water, and dried. The 2,6-dimercapto-3-methyl-1,4-thiopyrone weighed 7 grams and melted at 137 C.

. Example II The 2,6-dimercapto-3-methyl-1,4-thiopyrone HS SE was prepared from methyl ethyl ketone, carbon disulfide and potassium hydroxide.

A carbon tetrachloride suspension of 0.0398 mole of this dimercaptan was treated at 0 C. for three hours with 0.0796 mole of n-dodecyl sulfenyl chloride (prepared by chlorinating n-dodecyl mercaptan). The reaction mixture was washed with dilute alkali and with water and then was stripped of carbon tetrachloride by nitrogen blowing at 220 F. The product was a viscous liquid containing 23.5 percent S. Theoretical for Example 111 A 5.91 gram sample of the product described in Example II was heated with 0.64 gram of sulfur at C. for 1 /2 hours. The product was a dark brown liquid containing 34.3 percent S. This sulfurized material was tested at 0.75 percent concentration in a solvent extracted SAE 30 grade oil (containing about 3 percent detergent). The blend gave 6 mg. silver loss in the EMD test and SSCT losses of 134 mg. at 48 hours and 168 mg. at 72 hours.

Example IV V V 2,6-dimercapto-3,S-diphenyl 1,4 thiopyrone was prepared as follows: I r I p A mixture of 200 g. dibenzyl ketone, 350 ml. carbon disulfide, and 600 g. potassium hydroxide flakes were stirred at room temperature. After a few minutes a vigorous reaction ensued and the mass solidified. It was allowed to stand for 3 hours, dissolved in water, and acidified carefully with hydrochloric acid. A resin precipitated first; this was filtered OH, and the product obtained by acidification of the filtrate with excess acid. The crystals were collected on a filter, washed and dried, and recrystallized from toluene, giving 156 g. orange 2,6-dimercapto-3,S-diphenyl-1,4-thiopyrone melting at 155 C. Analysis.Calculated for C H S O: C, 62.2; H, 3.7; S, 29.28; neut. equiv., 164. Found: C, 62.25; H, 4.0; S, 28.9; neut. equiv., 160.

Example V 2,6-dimercapto-3,S-diphenyl-1,4-thiopyrone (JOE. COH

HS SH was prepared from dibenzylketone, carbon disulfide and potassium hydroxide. Nine grams of the thiopyrone was added to the solution of 0.55 mole of n-hexyl sulfenyl chloride in 50 cc. of carbon tetrachloride. The mixture was heated at 90-100 F. for V2 hour. The reaction mixture was washed with dilute alkali and with water and then was stripped of carbon tetrachloride in vacuo. The crude reaction product is a very viscous yellow oil and contained 28.1% sulfur. The product was tested at 0.75% concentration level in solvent extracted SAE-SO grade Mid-Continent oil containing about 3% of a detergent of the neutralized phosphorus sulfide-polybutene reaction product type. The oil gave a bright EMD silver strip and SSCT weight losses of 89 milligrams at 48 hours and 123 milligrams at 72 hours.

6 Calculated for CeHs CIHI 5 cuuu-s-s s-s-ctnu References Cited in the file of this patent UNITED STATES PATENTS Weiss Jan. 31, 1928 OTHER REFERENCES Arndt et al.: Beriche der Deut. Chem. GeselL, vol. 648, 30 pages 2393-7 (1930).

Asker et al.: Chem. Abstract, vol. 39, page 3283 (1945).

Asker et al.: Chem. Abstract, vol. 40, page 6469 (1946). 35 Barbenkus et al.: J. Org. Chem., vol. 16, pages 1047-9 

1. 2,6-BISALKYL DITHIO-1,4-THIOPYRONE WHEREIN THE ALKYL GROUP HAS 1 TO 20 CARBON ATOMS. 